-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello, I've converted FlightGear to use OSG's database pager. While I'm happy that it works at all, I've noticed that it can take a very long time (several seconds) to load in a single terrain tile which does not have very much data by modern standards. I believe the problem is excessive (re)compilation of GL objects.
Some background: I'm not using PagedLOD, but am making explicit requestNodeFile calls from FlightGear's existing tiling code. Actually, I've subclassed DatabasePager to support explicit delete requests too. I don't think that this usage pattern changes much with respect to the behaviour I'm seeing. When I set OSG_DO_PRE_COMPILE=no the tile times are much more reasonable (300 - 500 ms). Also, setting OSG_MAXIMUM_OBJECTS_PER_FRAME to higher values lowers the tile time. Both these changes produce noticeable jerks in the visuals. I think it's clear that the slow load times are caused by a storm of GL compile operations building up on the DatabasePager's queue. The terrain in FlightGear is polygon meshes with textures from a material library plus models loaded from the file system. Most of these models are shared with other tiles, so there is a lot of potential for sharing. We use the object cache in the file loader for these models, and the subgraph for the whole tile, including terrain and models, is built in the ReaderWriter::readNode method for the top-level tile file. So... I notice that DatabasePager::FindCompileableGLObjectsVisitor doesn't check if the object is already compiled, so I think our shared models and textures are being recompiled in every new tile that is loaded. This might not be very expensive for textures, but by default only 4 objects are compiled per frame, so it slows down the loading of the tile. The compileGLObjects method for osg::Drawable doesn't check if its object is already compiled (probably by design), and I imagine that compiling display lists could be expensive. Also, I've noticed that the SharedStateManager is called in the update traversal late in the loading process, after objects have been compiled. Is there any reason that this can't be done earlier, in the pager thread, potentially eliminating the need for some compilation? What are people doing with material and model libraries and paging? Do you live with vertex arrays and "precompile" textures, relying only on the SharedStateManager? I'd rather not give up on display lists just yet. Thanks, Tim -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iD8DBQFHMyTOeDhWHdXrDRURAvWLAKCoBPTSun+pegT+naicyUfnnabG4gCfWCeo kAcwiB7SuyTYk/NiaeJkwAs= =5ClR -----END PGP SIGNATURE----- _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
